Future flights to Mars will certainly be expensive. But according to Elon Musk, a ticket to the Red Planet and back may cost passengers less than $100,000 — assuming enough people want to make the trip.

On Sunday, the CEO of SpaceX offered his thoughts on how much consumers would need to save for a Mars trip. In a Twitter thread, Musk said he was confident the ticket could one day cost less than $500,000, and possibly even lower than $100,000.

Still, the final cost will be “very dependent” on the volume of travelers, Musk added. But if all goes well, the prices will be “low enough that most people in advanced economies could sell their home on Earth and move to Mars if they want,” he said.

Very dependent on volume, but I’m confident moving to Mars (return ticket is free) will one day cost less than $500k & maybe even below $100k. Low enough that most people in advanced economies could sell their home on Earth & move to Mars if they want.

Musk’s price estimate should be taken with some skepticism. His company is still in the early stages of designing an actual interplanetary craft that can safely carry humans beyond the Earth. Nevertheless, SpaceX has some pretty ambitious goals; the company plans on sending its first manned mission to the Moon in 2023, which will be followed up by a separate human-crewed mission to Mars in 2024.

To make interplanetary travel (somewhat) affordable, SpaceX has been focused on making its rocket technology reusable. It also wants to load as many as 100 paying passengers on board each Mars flight.

Back in 2017, Musk also offered some cost estimates for a ticket to Mars. “Assuming optimization over time, we are looking at a cost per ticket of less than $200,00, maybe as little as $100,000 over time, depending upon how much mass a person takes,” he said in an article in New Space.

At the time, Musk made the estimate by calculating that it’d cost about $140,000 per ton for a SpaceX trip to Mars. “If a person plus their luggage is less than that, taking into account food consumption and life support, the cost of moving to Mars could ultimately drop below $100,000,” he added.

The SpaceX ships will also travel back and forth between Mars and Earth. So return tickets from the Red Planet will be free, Musk said in his tweet on Sunday.